The present invention is based upon the discovery that a simple, efficient, open, partial conversion system for the production of liquid natural (LNG) can be provided if high pressure natural gas, taken directly from a well head or other appropriate source and cleaned (if required), is immediately thereafter split into two high pressure flow portions. The first high pressure flow portion is the source of the liquid natural gas fraction. The first flow portion is, itself, divided into two flow parts which are cooled in first and second heat exchangers, respectively, and then recombined. The recombined first flow portion is throttled into a liquid natural gas collector wherein a part of the first flow portion flashes to liquid natural gas. The gaseous remainder of the first flow portion within the liquid natural gas collector is used as a coolant for the second heat exchanger and is thereafter conducted to a receiver. The receiver may be of any appropriate type including a pipeline, the inlet of a gas turbine, the inlet of a chemical process, a burner head, a pump inlet, or the like. The vent remainder from the liquid natural gas tank is at a pressure equal to or slightly greater than the pressure within the receiver. The second flow portion is reduced in pressure in an expander to a pressure level less than that of the receiver to provide maximum cooling for the first heat exchanger to increase liquid natural gas production. Thereafter, the second flow portion is raised in pressure to a level equal to or greater than that of the receiver by a compressor run by work from the expander, and is introduced into the receiver.
Prior art workers have devised many types of partial conversion and total conversion systems for the production of liquid natural gas. This is exemplified in U.S. Pat. No. 3,735,600 where an open cycle is taught utilizing well head gas. In this system, however, once the well head gas has been purified, it is not immediately split into two flow portions. The arrangement of the equipment components differs from that of the present invention, as do the steps performed by the reference system.
Other prior art natural gas liquification systems are taught, for example, in U.S. Pat. No. 3,818,714 and U.S. Pat. No. 4,970,867, both of which are exemplary of the more complex prior art approaches.